BACKGROUND: The effect of nail polish on pulse oximetry measurements in non-hypoxic subjectshas been studied extensively. Some studies found that nail polish decreased pulse-oximetry (SpO2)values, whereas others found no effects from nail polish. OBJECTIVE: To determine if nail polishaffects SpO2 measurements in mildly hypoxic subjects. METHODS: At high altitude, 5 investigators,whose mean oxygen saturation was 91.3% (mild hypoxia), and with 2 brands of pulse oximeter andoximetry probe, obtained SpO2 measurements from a finger with nail polish and from the matchingfinger on the opposite hand without nail polish. We tested 9 different nail-polish colors and made210 pairs of SpO2 measurements. RESULTS: The mean SD SpO2 values from the fingers with andwithout nail polish, respectively, were 91.4 4.1% and 91.2 3.5% (difference 0.2 3.2%, 95%confidence interval 0.2% to 0.4%). CONCLUSIONS: With the pulse oximeters and oximetryprobes we tested, nail-polish had no significant effect on SpO2 in mildly hypoxic healthy subjects. Keywords: pulse oximetry, SpO2, nail polish, hypoxia, high altitude. [Respir Care 2008;53(11):14701474. 2008 Daedalus Enterprises]

Introduction

Pulse oximetry is an essential monitoring technology.Clinical decisions are often made based on pulse oximetryoxygen saturation (SpO2) measurements. Pulse oximetryworks by transmitting light onto one side of a digit (orother tissue appendage) and sensing the light transmissionon the opposite side of the digit. Standard pulse oximetryuses 2 light sources and 2 sensors. The red light source isvisible. The infrared light source is invisible. Changes inlight transmission through the digit permit the pulse oxime-ter to calculate oxygenation, based on the assumption thathemoglobin A is pulsing through the capillaries. The tech-nical aspects of pulse oximetry have been summarized by

others.1,2 New developments in pulse oximetry are im-proving its capabilities.

Since pulse oximetry probes are most commonly ap-plied over the fingernails, it has been a concern that nailpolish impedes light transmission. Previous studies havereported conflicting results (Table 1). Earlier studies foundthat some nail-polish colors reduced SpO2 by clinicallyimportant percentages,4-6 but more recent studies foundSpO2 measurements accurate even with opaque nail-polishcolors, including black, blue, and purple.8-11 Controversyremains, because the earlier studies found SpO2 decreasesof 510%, whereas in the more recent studies the SpO2decrease was 2%. All those studies used only non-hypoxic subjects.

We studied the accuracy of SpO2 measurements throughnail polish in mildly hypoxic subjects. SpO2 measurementsuse the color of the blood to measure oxygenation, so ahypoxic subject could have different light-absorption char-acteristics that might interact differently with certain nail-polish colors. For example, red nail polish could falselyincrease SpO2 readings, and blue and purple nail polishcould have the opposite effect. The effect of nail polish onSpO2 in non-hypoxic patients cannot necessarily be extrap-olated to hypoxic patients.

Loren G Yamamoto MD MPH MBA is affiliated with the Emergency De-partment, Kapiolani Medical Center For Women And Children, and with theDepartment of Pediatrics, John A Burns School of Medicine, University ofHawaii at Manoa, Honolulu, Hawaii.

The authors report no conflicts of interest related to the content of this paper.

Hypoxia was most conveniently induced by conductingthe study at high altitude. The summit of Haleakala Na-tional Park, Maui, Hawaii, at 3,048 m, is easily accessibleby car. The calculated air pressure is 523 mm Hg (com-pared to 760 mm Hg at sea level). At 523 mm Hg, a 0.21fraction of inspired oxygen yields an ambient PO2 of110 mm Hg (compared to 160 mm Hg at sea level). Thearterial PO2 at 3,048 m is approximately 5570 mm Hg.

The 5 study subjects (ages 50, 49, 20, 17, and 15) eachapplied nail polish (Table 2) to the digits of one hand. Thecorresponding digits on the other (control) hand had nonail polish. Two coats of nail polish were applied, andeach coat was allowed to dry before applying the next coator the pulse oximeter probe. SpO2 measurements were madeserially on the nail-polished digits and the non-nail-pol-ished (control) digits (same digit on the opposite hand, notnecessarily in that order). The measurements were con-ducted in a sheltered environment (an observation enclo-sure or a vehicle), because at the summit of Haleakala theoutdoor temperature is cold, which affects perfusion. Mostof the measurements were made with the subjects at rest,after achieving an oxygenation steady state. We also madesome measurements following a brief jog or brisk walk.

We used 2 pulse oximeter models: RDS1, Masimo, Irvine,California, and N20, Nellcor, Pleasanton, California. A dis-posable neonatal digit probe and a reusable adult clip digitprobe were used with the Masimo RDS1. With each RDS1measurement we also recorded the perfusion index, which isthe percentage of pulsatile signal to non-pulsatile signal. Witheach Nellcor N20 measurement we recorded the number ofperfusion bars; in Nellcors perfusion-measurement sys-tem, the maximum number of bars is 14. The purpose ofusing 2 different pulse oximeter models and different probeswas to study whether observed differences were consistentbetween the different pulse oximeters and probe types.

The pulse oximetry probes were applied in an anterior-posterior direction only (no oblique or lateral orientationmeasurements). The anterior-posterior alignment maxi-mizes the effect of the nail polish. Each digit was mea-sured with the probes light on the nail side of the digit,then the measurement was repeated with the light on thepad (palm) side of the digit. This was done to confirm thatthe nail polish versus control comparisons were consistentbetween the different methods of applying the probe.

Pulse oximetry measurements are continuous and notalways in a perfectly steady state. We observed the nu-meric values and the pulsation/perfusion data and recorded

Table 1. Studies of the Effect of Nail Polish on Pulse Oximetry Measurements

First Author Year Pulse Oximeter Summary

Kataria3 1986 Nellcor, model not specified Nail polish (color not specified) had no effect on SpO2.Rubin4 1988 Ohmeda Biox 3700 31 nail-polish colors were tested on one subject. Only the

the most dominant value (the most apparently correctvalue), as we do when reading SpO2 values in the clinic.

Our measurement sampling was optimized to comparethe nail-polished and non-nail-polished digits by alwayspairing a nail-polish measurement with a non-nail-polishmeasurement, with the same pulse oximeter and probetype for each pair of measurements. We did not performsimilar pairing with pulse oximeter types, pulse oximeterprobe types, or nail-polish colors, which made the compari-sons between oximeter types, probe types, and nail-polishcolors potentially subject to unintentional sampling bias.

This study was approved by the institutional reviewboard of Hawaii Pacific Health.

Results

We took 210 paired SpO2 measurements with 5 investi-gators. The mean nail-polish and non-nail-polish SpO2 val-ues, respectively, were 91.4 4.1% and 91.2 3.5%(mean difference 0.2 3.2%, 95% confidence interval0.2% to 0.4%). One hundred forty-four measurementswere made at rest, and 66 were made following a brief jogor a brisk walk (Tables 3 and 4). Although the differentnail-polish colors had di